Аль-Джабр: Основополагающий труд по алгебре IX века

Seminal Arabic treatise on algebra (c. 820 CE)

Al Jabr (Arabic: الجبر), also known as The Compendious Book on Calculation by Completion and Balancing (الكتاب المختصر في حساب الجبر والمقابلة, al Kitāb al Mukhtaṣar fī Ḥisāb al Jabr wal Muqābalah; or Liber Algebræ et Almucabola), is an Arabic mathematical treatise on algebra written in Baghdad around 820 by the Persian polymath Al Khwarizmi. It was a landmark work in the history of mathematics, with its title being the ultimate etymology of the word "algebra" itself, later borrowed into Medieval Latin as algebrāica. Al Jabr provided an exhaustive account of solving for the positive roots of polynomial equations up to the second degree. It also introduced the fundamental concept of "reduction" and "balancing" (which the term al jabr originally referred to), the transposition of subtracted terms to the other side of an equation, i. e. the cancellation of like terms on opposite sides of the equation. Translated into Latin by Robert of Chester in 1145, it was used until the sixteenth century as the principal mathematical textbook of European universities. Several authors have also published texts under this name, including Abu Hanifa Dinawari, Abu Kamil, Abū Muḥammad al ʿAdlī, Abū Yūsuf al Miṣṣīṣī, 'Abd al Hamīd ibn Turk, Sind ibn ʿAlī, Sahl ibn Bišr, and Šarafaddīn al Ṭūsī.

R. Rashed and Angela Armstrong write:
Al Khwarizmi's text can be seen to be distinct not only from the Babylonian tablets, but also from the Diophantus' Arithmetica. It no longer concerns a series of problems to be resolved, but an exposition which starts with primitive terms in which the combinations must give all possible prototypes for equations, which henceforward explicitly constitute the true object of study. On the other hand, the idea of an equation for its own sake appears from the beginning and, one could say, in a generic manner, insofar as it does not simply emerge in the course of solving a problem, but is specifically called on to define an infinite class of problems. J. J. O'Connor and E. F. Robertson wrote in the MacTutor History of Mathematics archive:
Perhaps one of the most significant advances made by Arabic mathematics began at this time with the work of al Khwarizmi, namely the beginnings of algebra. It is important to understand just how significant this new idea was. It was a revolutionary move away from the Greek concept of mathematics which was essentially geometry. Algebra was a unifying theory which allowed rational numbers, irrational numbers, geometrical magnitudes, etc., to all be treated as "algebraic objects". It gave mathematics a whole new development path so much broader in concept to that which had existed before, and provided a vehicle for future development of the subject. Another important aspect of the introduction of algebraic ideas was that it allowed mathematics to be applied to itself in a way which had not happened before.

The book was a compilation and extension of known rules for solving quadratic equations and for some other problems, and considered to be the foundation of algebra, establishing it as an independent discipline. The word algebra is derived from the name of one of the basic operations with equations described in this book, following its Latin translation by Robert of Chester.

Al Khwārizmī explicates the Jewish calendar and the 19 year cycle described by the convergence of lunar months and solar years.